A prettier plugin for the Ruby programming language
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Prettier Ruby

Prettier for Ruby

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@prettier/plugin-ruby is a prettier plugin for the Ruby programming language. prettier is an opinionated code formatter that supports multiple languages and integrates with most editors. The idea is to eliminate discussions of style in code review and allow developers to get back to thinking about code design instead.

Under the hood @prettier/plugin-ruby uses Ruby's own ripper library which allows this package to maintain parity with the existing Ruby parser. @prettier/plugin-ruby supports Ruby versions 2.5, 2.6, and trunk.

For example, the below code segment:

          a.transpose.each{ |a|
             |i|print i==49?\

when run through @prettier/plugin-ruby will generate:

d = [
a, s = [], $*[0]
s.each_byte { |b| a << ('%036b' % d[b.chr.to_i]).scan(/\d{6}/) }
a.transpose.each do |a|
  a.join.each_byte { |i| print i == 49 ? ($*[1] || '#') : 32.chr }

Getting started

First, your system on which you're running is going to need a couple of things:

  • ruby 2.5 or newer - there are a lot of ways to install ruby, but I recommend rbenv
  • node 8.3 or newer - prettier is a JavaScript package, so you're going to need to install node to work with it
  • npm or yarn - these are package managers for JavaScript, either one will do

Second, you're going to need to list @prettier/plugin-ruby as a JavaScript dependency from within whatever project on which you're working.

If you do not already have a package.json file in the root of your repository, you can create one with:

echo '{ "name": "My Project" }' > package.json

After that you can add prettier and @prettier/plugin-ruby to your package.json devDependencies by running npm install --save-dev prettier @prettier/plugin-ruby if you are using npm or yarn add --dev prettier @prettier/plugin-ruby if you are using yarn.

Finally, you can install your dependencies using either npm install for npm or yarn install for yarn.

Now, you can run prettier to tidy up your ruby files! Verify by running against a file:

./node_modules/.bin/prettier --write path/to/file.rb

If you're happy, you can can run prettier on an entire codebase:

./node_modules/.bin/prettier --write '**/*.{rb,rake}'

Note that you can also install prettier globally with npm install -g prettier or you can add ./node_modules/.bin to your $PATH so you don't need to reference the executable from the directory each time.


Below are the options (from src/ruby.js) that @prettier/plugin-ruby currently supports:

Name Default Description
printWidth 80 Same as in Prettier (see prettier docs).
tabWidth 2 Same as in Prettier (see prettier docs).
addTrailingCommas false Adds a trailing comma to array literals, hash literals, and method calls.
inlineConditionals true When it fits on one line, allows if and unless statements to use the modifier form.
inlineLoops true When it fits on one line, allows while and until statements to use the modifier form.
preferHashLabels true When possible, uses the shortened hash key syntax, as opposed to hash rockets.
preferSingleQuotes true When double quotes are not necessary for interpolation, prefers the use of single quotes for string literals.

Any of these can be added to your existing prettier configuration file. For example:

  "preferSingleQuotes": false

Or, they can be passed to prettier as arguments:

./node_modules/.bin/prettier --prefer-single-quotes false --write '**/*.{rb,rake}'


After checking out the repo, run yarn and bundle to install dependencies. Then, run yarn test to run the tests. You can pretty print a Ruby source file by running yarn print [PATH].

Useful resources for understanding the AST structure are:


Bug reports and pull requests are welcome on GitHub at https://github.com/prettier/plugin-ruby.


The package is available as open source under the terms of the MIT License.


Kevin Deisz